Achieving Fast Ion/Electron Transportation and Smooth Phase Transition in Polyanion Cathode by the High Entropy Strategy

Abstract

Polyanion compounds arouse significant interest as cathode materials for sodium-ion batteries due to their large 3D lattice structures and stable frameworks. Nonetheless, it remains a great challenge for polyanion cathodes to achieve both considerable rate capability and long-term cycling lifespan. Herein, a high entropy NASICON-type cathode, Na_3.6VMn_0.4Fe_0.4Ti_0.1Zr_0.1(PO₄)₃ (HE-NVMFTZP), is successfully synthesized for the first time and exhibits superior sodium storage performance. Specifically, it delivers a reversible capacity of 110 mAh g⁻¹, remarkable rate capability (78.5 mAh g⁻¹ even at 20 C), and an ultralong lifespan (80.6% after 10 000 cycles at 10 C), which outperforms all the reported metal-substituted NASICON electrodes. Moreover, in an expanded voltage window of 1.5–4.3 V, the HE-NVMFTZP electrode delivers an impressive capacity of 177.4 mAh g⁻¹ (≈494 Wh kg⁻¹). Comprehensive experimental characterizations and first-principles calculations reveal that the high entropy effect facilitates ion/electron transportation and alleviates volume expansion and phase transition during the charge/discharge process. This work provides a facile high entropy strategy on the local structural engineering of polyanion cathodes to effectively boost the sodium storage performance and can shed light on the design of stable and high-capacity cathode materials.